[PATCH] SPI: per-transfer overrides for wordsize and clocking

Some protocols (like one for some bitmap displays) require different clock
speed or word size settings for each transfer in an SPI message. This adds
those parameters to struct spi_transfer.  They are to be used when they are
nonzero; otherwise the defaults from spi_device are to be used.

The patch also adds a setup_transfer callback to spi_bitbang, uses it for
messages that use those overrides, and implements it so that the pure
bitbanging code can help resolve any questions about how it should work.

Signed-off-by: Imre Deak <imre.deak@nokia.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/spi/spi_bitbang.c

@@ -138,13 +138,51 @@ static unsigned bitbang_txrx_32(
 	return t->len - count;
 }
 
+static int
+bitbang_transfer_setup(struct spi_device *spi, struct spi_transfer *t)
+{
+	struct spi_bitbang_cs	*cs = spi->controller_state;
+	u8			bits_per_word;
+	u32			hz;
+
+	if (t) {
+		bits_per_word = t->bits_per_word;
+		hz = t->speed_hz;
+	} else {
+		bits_per_word = 0;
+		hz = 0;
+	}
+
+	/* spi_transfer level calls that work per-word */
+	if (!bits_per_word)
+		bits_per_word = spi->bits_per_word;
+	if (bits_per_word <= 8)
+		cs->txrx_bufs = bitbang_txrx_8;
+	else if (bits_per_word <= 16)
+		cs->txrx_bufs = bitbang_txrx_16;
+	else if (bits_per_word <= 32)
+		cs->txrx_bufs = bitbang_txrx_32;
+	else
+		return -EINVAL;
+
+	/* nsecs = (clock period)/2 */
+	if (!hz)
+		hz = spi->max_speed_hz;
+	cs->nsecs = (1000000000/2) / hz;
+	if (cs->nsecs > MAX_UDELAY_MS * 1000)
+		return -EINVAL;
+
+	return 0;
+}
+
 /**
  * spi_bitbang_setup - default setup for per-word I/O loops
  */
 int spi_bitbang_setup(struct spi_device *spi)
 {
 	struct spi_bitbang_cs	*cs = spi->controller_state;
 	struct spi_bitbang	*bitbang;
+	int			retval;
 
 	if (!spi->max_speed_hz)
 		return -EINVAL;
@@ -160,25 +198,14 @@ int spi_bitbang_setup(struct spi_device *spi)
 	if (!spi->bits_per_word)
 		spi->bits_per_word = 8;
 
-	/* spi_transfer level calls that work per-word */
-	if (spi->bits_per_word <= 8)
-		cs->txrx_bufs = bitbang_txrx_8;
-	else if (spi->bits_per_word <= 16)
-		cs->txrx_bufs = bitbang_txrx_16;
-	else if (spi->bits_per_word <= 32)
-		cs->txrx_bufs = bitbang_txrx_32;
-	else
-		return -EINVAL;
-
 	/* per-word shift register access, in hardware or bitbanging */
 	cs->txrx_word = bitbang->txrx_word[spi->mode & (SPI_CPOL|SPI_CPHA)];
 	if (!cs->txrx_word)
 		return -EINVAL;
 
-	/* nsecs = (clock period)/2 */
-	cs->nsecs = (1000000000/2) / (spi->max_speed_hz);
-	if (cs->nsecs > MAX_UDELAY_MS * 1000)
-		return -EINVAL;
+	retval = bitbang_transfer_setup(spi, NULL);
+	if (retval < 0)
+		return retval;
 
 	dev_dbg(&spi->dev, "%s, mode %d, %u bits/w, %u nsec\n",
 			__FUNCTION__, spi->mode & (SPI_CPOL | SPI_CPHA),
@@ -246,6 +273,8 @@ static void bitbang_work(void *_bitbang)
 		unsigned		tmp;
 		unsigned		cs_change;
 		int			status;
+		int			(*setup_transfer)(struct spi_device *,
+						struct spi_transfer *);
 
 		m = container_of(bitbang->queue.next, struct spi_message,
 				queue);
@@ -262,13 +291,28 @@ static void bitbang_work(void *_bitbang)
 		tmp = 0;
 		cs_change = 1;
 		status = 0;
+		setup_transfer = NULL;
 
 		list_for_each_entry (t, &m->transfers, transfer_list) {
 			if (bitbang->shutdown) {
 				status = -ESHUTDOWN;
 				break;
 			}
 
+			/* override or restore speed and wordsize */
+			if (t->speed_hz || t->bits_per_word) {
+				setup_transfer = bitbang->setup_transfer;
+				if (!setup_transfer) {
+					status = -ENOPROTOOPT;
+					break;
+				}
+			}
+			if (setup_transfer) {
+				status = setup_transfer(spi, t);
+				if (status < 0)
+					break;
+			}
+
 			/* set up default clock polarity, and activate chip;
 			 * this implicitly updates clock and spi modes as
 			 * previously recorded for this device via setup().
@@ -325,6 +369,10 @@ static void bitbang_work(void *_bitbang)
 		m->status = status;
 		m->complete(m->context);
 
+		/* restore speed and wordsize */
+		if (setup_transfer)
+			setup_transfer(spi, NULL);
+
 		/* normally deactivate chipselect ... unless no error and
 		 * cs_change has hinted that the next message will probably
 		 * be for this chip too.
@@ -406,6 +454,7 @@ int spi_bitbang_start(struct spi_bitbang *bitbang)
 		bitbang->use_dma = 0;
 		bitbang->txrx_bufs = spi_bitbang_bufs;
 		if (!bitbang->master->setup) {
+			bitbang->setup_transfer = bitbang_transfer_setup;
 			bitbang->master->setup = spi_bitbang_setup;
 			bitbang->master->cleanup = spi_bitbang_cleanup;
 		}

include/linux/spi/spi.h

@@ -31,13 +31,15 @@ extern struct bus_type spi_bus_type;
  * @master: SPI controller used with the device.
  * @max_speed_hz: Maximum clock rate to be used with this chip
  *	(on this board); may be changed by the device's driver.
+ *	The spi_transfer.speed_hz can override this for each transfer.
  * @chip-select: Chipselect, distinguishing chips handled by "master".
  * @mode: The spi mode defines how data is clocked out and in.
  *	This may be changed by the device's driver.
  * @bits_per_word: Data transfers involve one or more words; word sizes
  * 	like eight or 12 bits are common.  In-memory wordsizes are
  *	powers of two bytes (e.g. 20 bit samples use 32 bits).
  *	This may be changed by the device's driver.
+ *	The spi_transfer.bits_per_word can override this for each transfer.
  * @irq: Negative, or the number passed to request_irq() to receive
  * 	interrupts from this device.
  * @controller_state: Controller's runtime state
@@ -268,6 +270,10 @@ extern struct spi_master *spi_busnum_to_master(u16 busnum);
  * @tx_dma: DMA address of tx_buf, if spi_message.is_dma_mapped
  * @rx_dma: DMA address of rx_buf, if spi_message.is_dma_mapped
  * @len: size of rx and tx buffers (in bytes)
+ * @speed_hz: Select a speed other then the device default for this
+ *      transfer. If 0 the default (from spi_device) is used.
+ * @bits_per_word: select a bits_per_word other then the device default
+ *      for this transfer. If 0 the default (from spi_device) is used.
  * @cs_change: affects chipselect after this transfer completes
  * @delay_usecs: microseconds to delay after this transfer before
  * 	(optionally) changing the chipselect status, then starting
@@ -322,7 +328,9 @@ struct spi_transfer {
 	dma_addr_t	rx_dma;
 
 	unsigned	cs_change:1;
+	u8		bits_per_word;
 	u16		delay_usecs;
+	u32		speed_hz;
 
 	struct list_head transfer_list;
 };

include/linux/spi/spi_bitbang.h

@@ -30,6 +30,12 @@ struct spi_bitbang {
 
 	struct spi_master	*master;
 
+	/* setup_transfer() changes clock and/or wordsize to match settings
+	 * for this transfer; zeroes restore defaults from spi_device.
+	 */
+	int	(*setup_transfer)(struct spi_device *spi,
+			struct spi_transfer *t);
+
 	void	(*chipselect)(struct spi_device *spi, int is_on);
 #define	BITBANG_CS_ACTIVE	1	/* normally nCS, active low */
 #define	BITBANG_CS_INACTIVE	0